1. Technical Field
The disclosure relates to a Light Emitting Diode (LED) driving circuit, and more particularly to an Alternating-current-to-Direct-current (AC-to-DC) LED driving circuit.
2. Related Art
Recently, with increasing awareness of environmental protection, how to save energy has become an important topic. With respect to devices for illumination, LEDs, compared with common light emitting sources, are advantageous in having long service life, low power consumption, and being not easily damaged, and thus they are developed vigorously and play a critical role in daily life.
A conventional LED driving circuit includes a transformer, a Pulse Width Modulation (PWM) Integrated Circuit (IC), a constant-current circuit, and a feedback circuit. The transformer includes a primary side and a secondary side, and the feedback circuit includes a sensing resistor and a photocoupler. The PWM IC is electrically coupled to the primary side of the transformer, and the constant-current circuit is electrically coupled to the secondary side of the transformer. By the current passing trough the sensing resistor and the photocoupler, the feedback circuit couples a feedback signal to the PWM IC. The photocoupler receives the optical signal of the secondary side to generate a feedback signal, and the PWM IC receives the feedback signal to adjust the duty ratio of the PWM signal, wherein the duty ratio means the sustaining time of the PWM signal during which the voltage of the PWM signal remains high level in a duty cycle.
Accordingly, the LED driving circuit requires the photocoupler to couple the feedback signal to the PWM IC, thereby adjusting the duty ratio of the PWM signal output from the PWM IC. Therefore, the conventional LED driving circuit must employ more elements, a larger accommodation space is needed, and the manufacturing cost is also increased.